1. Field of the Invention
The invention relates to protection and detection of an electrical fault and more particularly of an electrical fault in an electrical distribution box. The invention applies advantageously but in a nonlimiting manner to electrical distribution in an aircraft.
2. Description of the Relevant Art
The distribution of the electrical energy in an aircraft is very hierarchical. The power is firstly produced on the basis of generators driven by motors. Next, this energy is conveyed to primary-distribution boxes. The energy is then distributed by cables exiting the primary-distribution boxes either directly to loads or to secondary-distribution boxes.
A first so-called hierarchical protection is known from the prior art and which is fitted at the level of each cable which exits the primary-distribution and secondary-distribution boxes and at the level of the generator and of the first distribution box. This first protection comprises, at the output of the distribution boxes, an isolator, a fuse or an isolator contactor. These protection elements allow opening in the case of a current overload. This first protection furthermore comprises at the level of the generator and of the primary-distribution box a control means for the generator and a command means for a line contactor of the primary-distribution box. These protection elements allow respectively shutdown of the generator and the opening of the line contactor in the case of a current overload.
To allow selectivity, that is to say to allow the shutdown of the distribution at a necessary and sufficient rank of the distribution, the protection elements have different triggering delays. Their triggering delay depends on their rank in the distribution. For example, the triggering delay for a fuse of a cable at the output of a secondary-distribution box will be less than the triggering delay for the generator control means. This makes it possible for just the protection element located directly upstream of the electrical fault to trigger, the protection elements further upstream not triggering. Thus, the triggering delay for the generator control means may reach 5 seconds. This time is, however, long enough to cause damage.
A second so-called differential protection is also known from the prior art and which comprises a measurement of the current upstream and downstream of a distribution line. In the case of absence of fault, the two measurements of current are equal. In the case of a fault, the current is different and it will be possible to locate this fault easily since it is located between the two measurement points. This protection is for example used to protect the cables of the generator. On the other hand this protection cannot easily be used to detect an internal short-circuit of a distribution box since a measurement is then necessary on each of the distribution lines emanating from the distribution box. Considering the number of lines which has to be measured and the disparity of the sensors used, high inadvertent risks of triggering the protection exist.